Although the secretory pathway is required for the survival of the individual cell and for the organism as a whole, the mechanism which governs vesicular transport is poorly understood. Recent data have shown that the rab family of ras-related small GTP-binding proteins are involved in the regulation of membrane traffic between distinct subcellular compartments. The long-term objective of this fellowship proposal is to characterize the role of the rab 1 gene product in protein export from the endoplasmic reticulum (ER) to the Golgi complex. It is only through the knowledge of normal cellular function that one can begin to understand where a defect could lead to a disease process. Structural information available for the ras protein has made it possible to map functional domains within the ras primary sequence. Site-directed mutations in the rab 1 gene analogous to known functional domains of ras will be generated. These mutated forms of rab (either encoded within a plasmid or a recombinant vaccinia virus) will be introduced into tissue culture cells, then evaluated for their effect on protein trafficking, in vivo. In addition, an in vitro transport assay developed in this laboratory which reconstitutes transport between the ER and cis Golgi compartments will be employed to study the biochemical function of rab 1 and to identify and isolate upstream or downstream effector molecules which interact with rab 1 and are required in the secretory pathway.